Study of Fe-C phase formulations through Fe self-diffusion during thin film growth

We studied diffusion process during the growth of Fe1-xCx (0 <= x <= 0.50) thin films at 300 K. The broadening of an introduced (Fe1-xCx)-Fe-57 thin layer obtained using secondary ion mass spectroscopy yielded concentration dependence of Fe self-diffusion. It suggests C occupies the grain boundary region and augments Fe self diffusion. After a critical value of x asymptotic to 0.04, it starts to slow down resulting in martensite phase and only amorphous Fe-C phases when x >= 0.20. These were combined with x-ray diffraction, atomic force microscopy (AFM), x-ray absorption near-edge structure (XANES) at Fe-L-2,L-3 and C K-edges, nuclear resonance scattering (NRS), SQUID vibrating sample magnetometer, and MOKE measurements. The local magnetic structure obtained using NRS reveals the formation of several phases including the martensite phase at the lower x to some fraction of the monoatomic FeC phase at the higher x. The XANES measurements show a charge transfer effect, indicating a self-organized multi-layered or clustered structure of phases. The surface morphology obtained from AFM measurements reveals the formation of clustered structures. The obtained results provide an important insight into the kinetics of iron carbide (Fe-C) phase formation and the influence of C concentration on the structural and magnetic properties of Fe-C thin films.